Bats dangle anti-malaria clues

Researchers are broadening studies on recent findings that a vast range of parasites, including plasmodium, are carried by bats inhabiting West African forests, with the mammals’ pathogenic tolerance seen as opening new potential for a malaria vaccine.

Scientists examined blood smears of more than 270 bats from 31 species in forests in Guinea, Liberia and Côte d’Ivoire, and found that 40 percent of the samples had infections with various malaria parasite strains, according to a study published in October.

“Surprisingly, we found two plasmodium species that are closely related to the rodent malaria plasmodium species… This close relationship of bat and rodent malaria parasites opens the door to test the bat plasmodium species as a new rodent malaria model system. This finding was unexpected when we started our investigation,” said Juliane Schaer, a co-researcher of the study.

Schaer, a PhD student at the Max Planck Institute for Infection Biology and the Museum of Natural History in Berlin, said their research was not directly linked to the malaria vaccine search, but noted its potential for furthering malaria vaccine studies. “We are investigating new samples from other African bat species. We still want to add information about the overall diversity of bat malaria parasites.”
Pathogen reservoir

“The discovery of the bat plasmodium species being closely related to the rodent malaria models represents a basic stage for ongoing studies,” Schaer told IRIN. “If, for example, it would be possible to isolate the parasites in the wild [at some time in the future] and adapt the parasite to the rodent lab model system, more advanced research could result, which might benefit the development of malaria vaccines.”

Bats host numerous pathogens, including the deadly Ebola and Marburg viruses, but have a high immunological tolerance. Exactly why they are a reservoir of a broad array of pathogens is unclear. It is thought that their long evolutionary history, species diversity - it is the second largest mammalian order after rodents - and large colony sizes could be responsible.

While rodent malaria parasites are found in areas of Central Africa and Nigeria, they have not been reported in these West African forests. The similarity of the two plasmodium species found in bats and rodents means the parasite samples can be transferred to lab rats. This, in turn, will allow the examination of bats’ robust pathogenic defence system.

The study noted that many rodent malaria strains used in experiments have been adapted to in-bred lab hosts for over three decades, hence presenting “un-natural parasite-host system.”

“Many studies focusing on vaccines and antimalarial drugs make use of mouse models. As the parasites found in bats are so similar to those in rodents, it may be easy to transfer them to mice and study them closer,” said a brief on the West African bats issued by the Max-Planck Institute for Infection Biology.

“We now know that malaria parasites have probably infected bats for millions of years and that their immune system has evolved to cope with the parasite. Knowing how they do this could be used to develop better vaccines against the disease,” explained Schaer.

Malaria risk

Around half of the world’s population is at risk of malaria. In 2010, the disease killed 660,000 people, most of them children in Africa, according to the World Health Organization. Clinical trials for antimalarial vaccines are ongoing in seven African countries and results are expected in late 2014.

To increase knowledge on human malaria, more studies will be needed on other parasite-hosting mammals, said Schaer. There are more than 550 malaria parasite species carried by birds, reptiles and other intermediate animal hosts. Only four malaria species are known to infect humans.

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